Cgs001@aol.com wrote:

> I was a little surprised that more people didn't pick up on this--thinner
> slides (ex: 3 microns) need to be stained longer....there just isn't the
> amount of cellular material there to absorb stain....also, years ago when the
> special stains were developed the ability to cut sections at 3 microns had
> not been achieved..therefore, the times used in the stains were all developed
> for those 5 micron sections....

    This was what I was taught and it has been my experience as well. I have
"done the experiment" with 0.25, 0.5, 1.0 and 2.0 micron plastic sections
(Araldite, Epon). I have also found that novice TEM students want to cut sections
as thin as possible, then have great difficulty getting enough contrast under the
beam. In both instances thicker sections = more tissue = better contrast, even
without any staining (other than osmium).
    In paraffin-embedded tissue, I suspect that what membranes remain are not
much of a barrier to diffusion, unless times are very short or the stain
molecules are very large.

Geoff
--
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Geoff McAuliffe, Ph.D.
Neuroscience and Cell Biology
Robert Wood Johnson Medical School
675 Hoes Lane, Piscataway, NJ 08854
voice: (732)-235-4583; fax: -4029
mcauliff@umdnj.edu
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